Segmented pipe couplings are well-known in the art, the respective coupling segments of such couplings being comprised of castings of a ductile iron.
The sealing gaskets that are to be positioned within the segmented pipe coupling commonly are formed from an elastomeric material, and include sealing lips, and if desired, a centrally located radially extending stem to be trapped between the adjacent ends of the pipes to be coupled by the coupling.
More commonly, the coupling segments include circumferentially extending keys at their respective opposite sides, the keys being for reception within grooves cut or otherwise formed in the exterior circumference of the pipes, the keys acting to resist axial stresses that are generated in the pipes, those axial stresses being absorbed by the coupling as a tensile or a compressive stress.
Other forms of such couplings have been proposed, in which the keys are separate from the coupling and are mechanically affixed to the external surface of the pipes, the keys then being received within grooves provided in the respective coupling segments.
Each of those constructions is encumbered with the disadvantage that either the pipes must be provided with cut or rolled grooves in their outer periphery, with the expense attendant thereon, or, the keys must be affixed mechanically to the pipe periphery, again with the expenses attendant thereon.
Such coupling segments are considered to be of minimal utility in the interconnection of pipes that have not been provided with grooves, or which have not been provided with mechanically attached keys, the reason being that the casting operation employed in the manufacture of the coupling segments, and, the material from which the coupling segments are cast are not conducive to the provision of sharp edges of a sufficient hardness for them to bite into the pipe exterior, in order to provide the required positive, as opposed to frictional, interconnection between the coupling and the respective pipes or fittings.